A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral end is attached to the substrate by means of a disc-like holdfast called the pedal disc, while in colonies of polyps it is connected to other polyps, either directly or indirectly. The oral end contains the mouth, and is surrounded by a circlet of tentacles.
Anthozoa is a class of marine invertebrates which includes the sea anemones, stony corals and soft corals. Adult anthozoans are almost all attached to the seabed, while their larvae can disperse as part of the plankton. The basic unit of the adult is the polyp; this consists of a cylindrical column topped by a disc with a central mouth surrounded by tentacles. Sea anemones are mostly solitary, but the majority of corals are colonial, being formed by the budding of new polyps from an original, founding individual. Colonies are strengthened by calcium carbonate and other materials and take various massive, plate-like, bushy or leafy forms.
Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a mouth is fringed with tentacles. Although some species are solitary, most are colonial. The founding polyp settles and starts to secrete calcium carbonate to protect its soft body. Solitary corals can be as much as 25 cm (10 in) across but in colonial species the polyps are usually only a few millimetres in diameter. These polyps reproduce asexually by budding, but remain attached to each other, forming a multi-polyp colony of clones with a common skeleton, which may be up to several metres in diameter or height according to species.
Tube-dwelling anemones or ceriantharians look very similar to sea anemones but belong to an entirely different subclass of anthozoans. They are solitary, living buried in soft sediments. Tube anemones live inside and can withdraw into tubes, which are composed of a fibrous material made from secreted mucus and threads of nematocyst-like organelles known as ptychocysts. Within the tubes of these ceriantharians, more than one polyp is present, which is an exceptional trait because species that create tube systems usually contain only one polyp per tube. Ceriantharians were formerly classified in the taxon Ceriantipatharia along with the black corals but have since been moved to their own subclass, Ceriantharia.
Duncanopsammia is a monotypic genus of stony corals. It is represented by the single species, Duncanopsammia axifuga, commonly called whisker coral, duncanops coral, or simply duncan coral. Individual polyps are fairly large with round skeletal bases (corallites) 10–14 millimetres (0.39–0.55 in) in diameter and larger central discs from which multiple tentacles radiate; the polyps form a structure branching at irregular intervals to form a large colony.
Corynactis californica is a brightly colored colonial anthozoan corallimorph. Unlike the Atlantic true sea anemone, Actinia fragacea, that bears the same common name, strawberry anemone, this species is a member of the order Corallimorpharia, and is the only member found in the North American West Coast. Other common names include club-tipped anemone and strawberry corallimorpharian. The anemone can live up to at least 50 meters deep on vertical rock walls, and at the bottom of kelp forests. It is known to carpet the bottom of some areas, like Campbell River in British Columbia, and Monterey Bay in California.
The Fungiidae are a family of Cnidaria, often known as plate corals. The family contains thirteen extant genera. They range from solitary corals to colonial species. Some genera such as Cycloseris and Fungia are solitary organisms, Polyphyllia consists of a single organism with multiple mouths, and Ctenactis and Herpolitha might be considered as solitary organisms with multiple mouths or a colony of individuals, each with its separate mouth.
Tubularia indivisa, or oaten pipes hydroid, is a species of large hydroid native to the northeastern Atlantic Ocean, the North Sea, Norwegian Sea, and the English Channel. The conical solitary polyps are found on dull yellow unbranched stems that reach 10 to 15 cm in height with a diameter of 1.5 cm (0.59 in). They may be fused to a small number of other individual stems at their bases. The pinkish to red polyps resemble flowers, having two concentric rings of tentacles, with the outer rings being paler and longer than the inner ring. At the center is a pale pink gonotheca. They are preyed upon by nudibranchs.
Dendrophylliidae is a family of stony corals. Most members are azooxanthellate and thus have to capture food with their tentacles instead of relying on photosynthesis to produce their food. The World Register of Marine Species includes these genera in the family:
Balanophyllia bonaespei is a species of solitary cup coral, a stony coral in the family Dendrophylliidae. It is an azooxanthellate species that does not contain symbiotic dinoflagellates in its tissues as most corals do.
Cynarina lacrymalis is a species of stony coral in the family Lobophylliidae. It is variously known as the flat cup coral, solitary cup coral, button coral, doughnut coral, or cat's eye coral. It is found in the western Indo-Pacific Ocean and is sometimes kept in reef aquaria.
Balanophyllia europea, called also scarlet coral or pig-tooth coral, is a small species of stony coral in the family Dendrophylliidae.
Leptopsammia is a genus of stony cup corals in the family Dendrophylliidae. Members of this genus are found at depths down to about 900 metres (3,000 ft). They are azooxanthellate, meaning that they do not contain symbiotic photosynthetic algae as do many species of coral.
Astroides is a genus of stony cup corals in the family Dendrophylliidae. It is monotypic and the only species is Astroides calycularis, which is endemic to the western Mediterranean Sea. The species was first described in 1766 by the German naturalist Peter Simon Pallas.
Megatrema anglicum is a species of acorn barnacle that grows in association with or semi-parasitically on corals and octocorals. It is found in the intertidal zone on the coasts of northwestern Europe and in the Mediterranean Sea.
Cladopsammia is a genus of stony cup corals in the family Dendrophylliidae. Members of this genus are found at depths down to about 470 metres (1,540 ft). They are azooxanthellate corals, meaning that they do not contain symbiotic photosynthetic dinoflagellates as do many species of coral.
Maasella is a genus of soft coral in the family Paralcyoniidae. It is monotypic, with only a single species, Maasella edwardsi. Usually of greenish brown or golden brown color, each polyp has eight pinnate tentacles. This soft coral is found in the Mediterranean Sea and the Atlantic Ocean, at depths of between 2 and 50 metres.
Polycyathus muellerae is a small species of coral in the family Caryophylliidae in the order Scleractinia, the stony corals. It is native to the northeastern Atlantic Ocean and the Mediterranean Sea. It is a large polyp, colonial coral and grows under overhangs and in caves as part of an assemblage of organisms suited to these poorly-lit sites.
Balanophyllia elegans, the orange coral or orange cup coral, is a species of solitary cup coral, a stony coral in the family Dendrophylliidae. It is native to the eastern Pacific Ocean. As an azooxanthellate species, it does not contain symbiotic dinoflagellates in its tissues in the way that most corals do.
